A common system for dispensing volatile materials such as perfumes or fragrances includes an impermeable reservoir containing a liquid mixture of the volatile materials. This reservoir has a narrow opening that supports a wick. The wick is inserted through the opening in the reservoir until one end of the wick contacts the liquid in the reservoir and the other end extends outside the reservoir into the surrounding atmosphere.
In operation, the liquid is absorbed by the fibers of the wick and is drawn upward through the wick fibers by microscopic capillary action. The liquid passes up the wick, through the wick opening in the reservoir and wets that portion of the wick that is outside the reservoir.
Since the surrounding atmosphere has a lower partial pressure (i.e. concentration) of volatile materials than the vapor inside the reservoir, the liquid evaporates from the wick outside the reservoir. As it evaporates, the microscopic capillary action causes additional liquid to be drawn up the wick to replace the evaporated liquid, thereby continuing the process of evaporation.
This reservoir and wick arrangement is not necessary to volatilize the liquid, however. An open pan or tray with a large surface area containing a quantity of the liquid would certainly evaporate the liquid material and do so at a much faster rate.
In most applications, however, the goal is not merely to evaporate the volatile liquid, but to evaporate the liquid in a controlled and linear manner over an extended period of time. This is the case with household fragrances. Most consumers would prefer to buy a volatile fragrance dispenser, place it in an area to be scented, and have that area scented at a constant level over an extended period of time, typically, on the order of days, weeks, or even months. For many consumers it is irritating when a volatile scent dispenser provides an overwhelming scent for the first few hours or days, then rapidly fades away to the merest suggestion of the original scent.
For this reason, a longstanding concern and key design goal for the volatile dispensing industry has been to devise volatile dispensers that generate longer lasting scents (in the case of scent dispensers), at a sufficient evaporation rate that are more evenly (linearly) dispensed over an extended period of time.
In order to be transported up a wick, a liquid must have a lower surface tension than the surface energy of the wick to permit the wick fibers to be wetted, and a low viscosity to permit the liquid to be transported through the fibers that comprise the wick via microscopic capillary action.
As a result, the volatile liquids used in volatile dispensers are typically mixtures of several other liquid components in addition to the active ingredient or ingredients that one wishes to dispense. Each additional component serves a specific function, either to increase volatility, to decrease viscosity, or to reduce the surface tension of the volatile liquid.
These additional liquid components collectively act as carriers to lift the active ingredient or ingredients from the surface of the liquid in the reservoir and up through the wick.
There are significant problems using these mixtures. The problems arise because the mixtures are just that—mixtures—and do not stay perfectly mixed as they evaporate. The carriers tend to evaporate sooner and at a faster rate than the dispensed liquid itself. While they do help carry the dispensed liquid up the wick, the carrier fluids tend to evaporate sooner. As a result, they leave significant amounts of the dispensed liquid within the wick itself and significant deposits on the end of the wick.
Over time, as the carrier is preferentially evaporated from the wick, the wick itself is increasingly filled with higher and higher concentrations of the dispensed liquid. This reduces the transport of both the carrier and the dispensed liquid and eventually causes the liquid transport up the wick to cease altogether.
As a result, the effective evaporation rate of volatile dispensers can drop by a factor of fifty percent or more over the emptying lifetime of a typical volatile dispenser. In sum, while the carriers can assist the transport of dispensed liquid, they still do not provide the linearity of dispensing that is desired.
What is needed, therefore, is and improved volatile material dispenser or volatizer that provides a more linear evaporation response. What is also needed is a volatile dispenser that reduces or eliminates the effect of selective evaporation. What is also needed is a volatile dispenser that provides an effective evaporation rate of dispensed material in a package that is small enough to be useable in and around the house.
It is an object of the present invention to provide such a dispenser.